1. Field of the Invention
This invention generally relates to low-cost, compact, photographic cameras and, more particularly, to special purpose, compact, dual focal length cameras operable in a wide angle mode for taking wider field of view photographs than normal and a telephoto mode for taking close-up photographs that have the appearance of distant scenes as observed through binoculars having a magnification in the range including 5.times.-8.times..
2. Description of the Prior Art
In the last few years, a significant market has developed for simple, low-cost 35 mm cameras of the "point and shoot" type. These cameras are available in both the conventional multiple-use configuration, which is adapted to have the end-user load and replace the film supply, and a single-use format which comes pre-loaded with film and is intended to be sent back to a factory for film processing.
Such single-use 35 mm cameras have become extremely popular because they are perceived as a convenient, low-cost alternative to conventional cameras with replaceable film capability. The single-use cameras typically come with a single lens having a focal length that provides a slightly wider angular view than is considered normal for 35 mm film (usually with a lens having a focal length approximately equal to the film diagonal to about 50 mm). Telephoto and panoramic versions of the single-use camera also are available. For prior art examples of such wide angle, telephoto and panoramic single-use cameras, reference is directed to U.S. Pat. No. 5,576,782 issued on Nov. 19, 1996 and entitled "LENS-FITTED PHOTO FILM UNIT FOR USE WITH TAKING LENSES OF DIFFERENT FOCAL LENGTH".
Also known in the prior art are single-use, dual focal length cameras having two taking lenses, each having a different focal length. Usually, these cameras include a wide angle lens for taking wide angle photographs and a telephoto lens for taking close up photographs of distant scenes. The wide angle lens typically has a focal length in the range of 30-40 mm, and the telephoto lens typically is in the short telephoto range of 70-90 mm, thus providing a modest telephoto to wide angle focal length ratio of about 2:1, or at best 3:1.
The wide angle lens is generally mounted on the front of camera forward of an unfolded, relatively short, direct optical path from the lens to the film plane, which is located at the back of the camera. Because the imaging optical path for the telephoto lens is approximately two to three times longer than that of the wide angle lens, and it is desirable to keep the size of the camera housing relatively compact, these cameras generally use two internal mirrors (usually one mirror is moveable) to define a compact, folded optical path between the telephoto lens and the film plane.
For examples of such dual focal length cameras, reference is directed to: U.S. Pat. No. 4,609,270 issued Sep. 2, 1986 and entitled "CAMERA WITH INTERCHANGEABLE TAKING LENSES"; U.S. Pat. No. 4,772,903 issued Sep. 20, 1988 and entitled "DUAL LENS CAMERA"; and U.S. Pat. No. 4,989,026 issued Jan. 29, 1991 and entitled "BIFOCAL CAMERA".
While these dual focal length cameras perform very well when operated in the telephoto mode for taking photographs of scenes or subjects at moderate distances, photographs taken of far away subjects, such as athletes at sporting events or performers at entertainment events, are very disappointing because the subjects of principal interest are relatively small in the photograph and still appear to be very distant.
To obtain a close-up view of distant subjects at such events, people will often use a pair of binoculars providing image magnification in the range of 5.times.-8.times.. However, when they take a photograph of the same scene using the dual focal length camera's 70-90 mm telephoto lens, the resultant photographic image of the scene is only about one-half to one-third the size of the image provided by the binoculars.
This invention is intended to fulfill an identifiable need for a compact, low-cost, dual focal length camera to be used in conjunction with binoculars of modest power at sporting, entertainment, or other events for taking close up photographs that have the appearance of distant scenes as observed through binoculars having a magnification in the range including 5.times.-8.times..
In binocular jargon, one often refers to the the width of the field covered at a distance of 1000 yards, and this ususally corresponds to the diameter of a circle since most binoculars have circular fields of view. To achieve field coverage comparable to 5.times.-8.times. binoculars at 1000 yards requires a telephoto lens whose focal length is approximately between 140 to 240 mm, which is substantially longer than the typical telephoto lens provided in such dual focal length cameras.
However, a dual focal length 35 mm camera incorporating a telephoto lens in the 140-240 mm focal length lens range would require an unacceptably large and ergonomically undesirable camera, even if one adopts the above noted prior art practice of using two internal mirrors to define a folded optical path between the telephoto lens and the camera's film plane.
Therefore, it is a principal object of this invention to provide a compact, dual focal lens camera which is operable in a telephoto mode to take close-up photographs that have the appearance of distant scenes as observed through binoculars having a magnification in the range including 5.times.-8.times..
Another object of this invention is to provide such a camera in which the telephoto optical system for taking such close-up photographs in configured in ways that fit into a compact camera housing that is ergonomically desirable and is only slightly larger than the housing used in conventional dual focal camera.
Yet another object of this invention is to provide such a camera that is inexpensive to manufacture thereby making it economically feasible to market the camera in a single-use camera configuration.
Another object of this invention is provide a compact, low-cost, dual focal length camera that is specially designed to be a complementary companion product for use in conjunction with a pair of low cost binoculars, such as those disclosed in U.S. patent application Ser. No. 08/320,920 filed on Oct. 11, 1994 and entitled "Low-Cost, Light-Weight, Compact Binoculars".
Another object of the invention is to provide a compact, dual focal length optical system that is capable of imaging onto a photodetector in telephoto and wide angle modes of operation.
Another object of the invention is to provide compact, single-use cameras with medium telephoto lenses.
Other objects of the invention will in part be obvious and will in part appear hereinafter. A full understanding of the invention will best be had from reading the detailed description to follow in connection with the detailed drawings.